The HK equivalent of Pure Direct seems to be "Surround Off" without the "DSP" option selected. On my 630, the Stereo button seems to cycle through :

Surround Off (no bass management, no surround processing)
Surround Off + DSP (bass management but no surround processing)
5 channel Stereo
7 channel Stereo

On the 525, the "pure analog, no digitizing" mode is selected by choosing "Large" for your main speakers and "Surround Off" for the processing mode.

See page 22 of the following link :

Click me, click me !!

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8